The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to structures for a field-effect transistor and methods of forming a structure for a field-effect transistor.
Device structures for a field-effect transistor generally include a source, a drain, and a gate electrode configured to switch carrier flow in a channel formed in a semiconductor body arranged between the source and drain. The semiconductor body and channel of a planar field-effect transistor are arranged beneath the top surface of a substrate on which the gate electrode is supported. When a control voltage exceeding a designated threshold voltage is applied to the gate electrode, the flow of carriers in the channel produces a device output current.
Nanosheet field-effect transistors have been developed as a type of non-planar field-effect transistor that may permit additional increases in packing density in an integrated circuit. The body of a nanosheet field-effect transistor includes multiple nanosheet channel layers that are arranged in a layer stack. The nanosheet channel layers are initially arranged in a layer stack with sacrificial layers containing a material (e.g., silicon-germanium) that can be etched selectively to the material (e.g., silicon) constituting the nanosheet channel layers. The sacrificial layers are etched and removed in order to release the nanosheet channel layers and to provide spaces for the formation of a gate stack. Sections of the gate stack may surround all sides of the individual nanosheet channel layers in a gate-all-around arrangement.
Nanosheet field-effect transistors may encounter difficulty in scaling because thinning silicon nanosheet channel layers may reach a thickness at which quantum confinement effects degrade performance. In addition, short channel effects may limit the ability to continue to shrink the gate length. As such, limits over electrostatic control for nanosheet field-effect transistors having silicon nanosheet channel layers may limit scaling.